Lateral flow assays (LFA) use a porous polymeric film, usually comprising nitrocellulose (cellulose nitrate) on a carrier plastic, to provide a wicking medium to transfer liquid that contains assay components from an origin through a region of immobilized ligands, wherein interaction of binding pairs and detection of bound ligand pairs can occur.
LFAs are commonly used as diagnostic test devices to detect the presence of biological molecules by a capillary action mechanism of flowing biomolecule solutions through a porous strip. As the sample passes through the strip's pores and regions containing a biomolecular ligand specific to an analyte of interest, any molecules of the analyte of interest, if present, will be bound and immobilized by the previously affixed biomolecular capture ligand. Labeling methods that allow visualization of the bound biomolecule complex can then provide determination of the presence or absence of the biomolecule of interest. In this way, a sample of unknown composition may be applied to the origin, and capillary action (wicking) moves the liquid through the length of the film strip.
One example LFA test is the human pregnancy test. Other common applications are related to the detection of toxic compounds, infectious diseases, allergens, chemical contaminants and illicit drugs, etc. LFA tests are particularly useful in the area of point-of-care testing, which eliminates the need of time-consuming laboratory work so that test results can be detected visually within a relatively short time frame, such as in 5-30 minutes. LFA tests are also used in academic and research settings to detect specific proteins of biomedical and chemical interest.
Methods to make such lateral flow assays devices as described above are described in WO00/08466 by Freitag et al. (U.S. Pat. No. 6,214,629 B1). Described therein is a diagnostic device that incorporates both a dry porous carrier in the form of a nitrocellulose sheet, and a housing for that carrier that incorporates a sample inlet.
However, the inventors herein have recognized potential issues with such systems. As one example, the LFA devices by Freitag et al. and others are cumbersome and labor intensive to produce because of the cutting and assembly steps required to fabricate the final device. LFA devices are typically constructed in a multi-step process in which the nitrocellulose film is cast to a large sheet, functionalized with immobilized capture ligands, blocked against further protein binding, cut into strips, and assembled into a single use device. The process is time consuming, and contributes a large fraction of the production cost as well as the introduction of variability.
In one example, the issues described above may be addressed by a lateral flow assay device, wherein the device is made by casting a polymer mixture containing nitrocellulose directly to a substrate or device housing. This direct casting method thus eliminates multiple processing and assembly steps. In another aspect, one or more combinations and formulations of the components of a polymer mixture, including, but not limited to a solvent, non-solvent, and nitrocellulose, as well as the conditions under which the mixture is allowed to polymerize and dry, may be regulated and altered to achieve a desired pore size and uniformity of a porous nitrocellulose strip. For example, the relative humidity and/or the temperature of the environment in which the nitrocellulose strip is cast and cured may be adjusted to regulate the rate at which volatile components of a polymer mixture evaporate. By adjusting the rate at which the volatile components evaporate, the resulting pore size of the nitrocellulose strip may be adjusted to a desired pore size. In this way, the resulting strip has wicking and biomolecular binding properties that allow development of desired lateral flow biomolecular detection assays.
In another example, a device may comprise a housing comprising an upper first portion and a lower second portion, the lower second portion further including a planar surface, a nitrocellulose matrix strip, the strip disposed on the planar surface, and one or more ligand regions included in the strip, the ligand regions comprising one or more ligands. In this way, separate sheets of nitrocellulose may be avoided, and thus improved manufacturing may be achieved. The strip may be of various forms, including linear, curved, S-shaped, sinuous, and/or angled.
In yet further examples, a method may comprise positioning a dispensing device a threshold vertical distance above a substrate, dispensing a liquid polymer mixture from the dispensing device onto a planar surface of the substrate, and while dispensing the polymer mixture, moving the dispensing from a first position to a second position. Further, the method may comprise, in response to the dispensing device reaching the second position, terminating the dispensing, and drying the mixture.
Another aspect includes a method for producing a nitrocellulose strip on a substrate by using a dispensing device; providing a removable framed mask on top of the substrate to define the shape, size and thickness of the strip; dispensing a nitrocellulose-based polymer mixture through the frame onto the substrate; and spreading the dispensed mixture with the dispensing head in a programmed fashion.
An advantage is the ability to produce nitrocellulose-based strips for LFA comprising a plurality of pores of a uniform size due to controlled evaporation of the components of the polymer mixture without the need for inefficient processing and assembly steps. This enables an automatable fabrication process that will result in more reproducible products than those currently available with multi-component devices assembled in a multi-step process.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.
Note that the drawings are not to scale, and that as such, other relative dimensions may be used. Further, the drawings may depict components directly or indirectly touching one another and in contact with one another and/or adjacent to one another, although such positional relationships may be modified, if desired. Further, the drawings may show components spaced away from one another without intervening components therebetween, although such relationships again could be modified, if desired.